In recent years, since ink-jet recording enables simple and less expensive formation of images, it has been applied to various printing fields such as photography, various kinds of printing, marking, and special printing such as color filters. Specifically, by employing ink-jet recording apparatuses which eject minute ink droplets and control them, ink-jet inks which result in an improved range of color reproduction, durability, as well as ejection adaptability, and specialized paper sheets of which ink absorbability, color forming properties of colorants and surface glossiness are markedly improved, it has become possible to result in image quality comparable to conventional silver salt photography.
However, in ink-jet image recording systems which necessitate specialized paper sheets, problems occur in which recording materials are limited and the cost of recording materials increases.
Specifically in offices, a system is increasingly demanded which is capable of performing full-color printing at a high rate without any limitation to recording materials (e.g., plain paper, coated paper, art paper, or double sided printing on plain paper).
Various studies have been conducted with regard to compositions of ink-jet inks capable of achieving higher speed printing, desired text reproduction on plain paper, resulting in no ink penetration to the back surface during printing (being the phenomena in which printed ink passes through the recording material and a printed image appears on the rear surface), no feathering, and no image bleeding, as well as resulting in quick penetration into the recording paper and rapid drying of the image.
As one of these methods, so-called water-based ink-jet inks are widely employed. When images are recorded on plain paper such as copy paper for electrophotography, high quality paper or medium quality paper, in addition to problems such as image penetration to the rear surface and feathering due to penetration, curling and cockling of images recorded on plain paper result in major problems.
In order to overcome the above drawbacks, an ink-jet recording method is disclosed (refer, for example, to Patent Document 1) which employs a penetration-improved ink by specifying the wetting time and the absorption coefficient of recording materials in the Bristow method. However, since colorants in the ink simultaneously penetrate into plain paper, this method results in problems, in which a decrease in image density as well as penetration to the rear surface is enhanced, resulting in unsuitability for both sided printing.
Further, ink-jet ink is disclosed (refer, for example, to Patent Document 2) which incorporates specified amide compounds, pyridine derivatives, imidazoline compounds or urea compounds as an anti-curling agent. However, this method results in problems in which clogging of the nozzle of a recording head tend to occur due to drying of liquid ink.
Still further, proposed is an ink-jet recording method to minimize the above curling (refer, for example, to Patent Document 3), in which curling balance is optimized by providing a solution containing water on the side opposite the image printing surface. However, this method is not fully adequate to print on two surface sides of the recording sheet. And further, this method may result in problems in which along with an increase in the adhered amount of ink as well as curl balance liquid onto plain paper, its strength is deteriorated, whereby jamming tends to occur during conveyance.
Still further, instead of using the water-based ink-jet ink, a solvent-based ink capable of achieving printing at a high rate has been studied. Namely, by employing an oil-based ink (being a solvent-based ink-jet ink), even though printed on plain paper, it is possible to achieve high speed printing due to quick penetration into recording materials, shorter drying time, and no curling of recording materials. However, problems occur in which text is not reproduced as desired and penetration to the rear surface results due to the fact that the solvent based ink easily penetrates plain paper. Especially, these problems were obstacles to print on two surface sides of a plain paper.                (Patent Document 1) Japanese Patent Publication Open to Public Inspection. (hereinafter referred to as JP-A) No. 10-316915        (Patent Document 2) JP-A No. 9-176538        (Patent Document 3) JP-A No. 10-272828        